In office buildings and other commercial settings where a number of separate telephone lines are provided in areas remote from an interface with telephone company lines or a central switchboard, telephone signals are typically carried to individual telephones by means of multiline trunk cables. These cables can be run from an intermediate distribution point where the individual lines are collected together to or towards a central location such as the switchboard or telephone company line interface. Modern installation practice is to provide "modular" telephone cables with connectors at either end for easy identification and connection of all wire ends. Each cable carries the wire pairs for one or more individual lines. Depending upon the type of service provided, two to four wire pairs are typically used for each line. Interfacing boards are also typically provided at intermediate distribution points for convenient break out of the individual lines carried by a trunk cable. Such boards provide a trunk connector for receiving the connector at the proximal end of the trunk cable and, a number of individual line connectors each adapted to mate with a modular plug on the end of an individual line cable. Circuitry on the board completes the connections between the wires of the individual line cable and the trunk cable. Individual telephone end units such as telephones are then installed at the remaining end of the individual line cable, again typically by means of a standard, modular connector at the end of the individual line cable which will receive a standard modular plug from a telephone or other end unit.
One longstanding problem has been the identification of individual lines at the end of the trunk cable remote from the individual line connections. Unless careful notes are taken during installation, it is necessary by some means to ascertain the location of each individual phone line in the multiwire cable supplying it. This must be known so that the phone company can wire and program the system for use at their end. Historically, Bell employees have "talked" these lines out. This requires two people, one at the individual phone location and one at the end of the multiwire cable. The man on the multiwire wire cable must "hunt" for the other at the individual phone location. There is the necessity to check as many as 50 individul wires by this method. The number and small size of the wires makes this a laborious process. The time-consuming nature of such an identification process has caused the installation and maintenance of the distribution lines to be particularly expensive.